The Company Valeo Vision is the proprietor of numerous patents relating to reflective surfaces which are capable of producing by themselves beams of given configurations, and in particular European standard type cruising beams which are of substantial width without any intervention by the cover lens of the headlamp. Such surfaces are entirely effective when they are used in cooperation with light sources that consist of incandescent filaments.
However, there is today a tendency to use, instead of filament lamps, discharge lamps which are known to produce a particularly high light output. Nevertheless, this type of light source has the disadvantage that the geometry of the pattern of emission of light by the source is not well controlled, so that when the above mentioned carefully defined reflective surfaces are used in conjunction with discharge lamps, there is a high degree of degradation of the photometry of the resulting light beam, in particular as regards the generation of a clean cut-off.
In addition, any cut-out, interruption or discontinuity in the surface of the reflector, which may be desirable in the case where it is required to generate portions of the beam having different positions within the final beam, and having different degrees of widthwise spread, will run the risk of giving rise, having regard to the high energy of the light source, to parasitic radiation which tends to dazzle the drivers of vehicles travelling in the opposite direction.
Thus, with a discharge lamp the designer has a natural tendency to continue to use entirely smooth reflective surfaces, which may be striated, and this imposes constraints on the technology.
This is why it has been proposed, in particular in United Kingdom patent specification GB 2 296 559, to place any cut-outs, interruptions or discontinuities, which may be present for example in the transition region between two zones of the reflector, in correspondence with shadows defined by masks associated with the light source. The arrangements described in that patent are however limited to the case where the reflective surfaces are parabolic. The zone of the reflector which forms the main part of the beam (i.e. an upper zone) has a surface which corresponds to the same paraboloid over its whole extent. The reflector is then unable to generate by itself a directly usable wide beam, so that the use of a striated cover lens is necessary, with the usual disadvantages of this type of lens, such as loss of light flux in the lens, limitations in the degree of spread that can be obtained using striations, and so on.